Between ten and 70 percent of cancer deaths in the U.S. may be attributed to diet. Many epidemiologic studies have suggested an association between cancer incidence and the consumption of specific foods. The validity of dietary assessment methods long used to study the diet-cancer hypothesis has never been rigorously established. An unequivocal understanding of the reliability of such methods is essential. This study proposes to assess the reliability of dietary recall among three subgroups of California Seventh-day Adventist men and women selected from two ongoing prospective studies and a completed nutrition substudy. We propose to reassess dietary intake by interviewing a random sample of 300 living cancer cases, 100 surrogates of deceased cases and 300 living matched controls, all from a prospective study for which extensive dietary and lifestyle data are known. This will enable us to assess seven and 23-year dietary recalls. We will reassess major nutrient estimates for 267 SNSS participants who completed a detailed food frequency questionnaire in 1973. These data will permit us to estimate the reliability of recall periods of seven, ten, and 23 years, to compare the recall reliability of cancer cases and non-cancer controls to determine the correlates of reliability, to determine how recall reliability varies by food and nutrient, to determine how long-term consistency in diet associates with past dietary recall, to determine the reliability of surrogate's recall of a proband's past food use, and to determine the characteristics which best distinguish between persons who reliably recall past food intake and those who do not. The comprehensive data base with its wealth of prospectively-collected information on diet and cancer affords a unique opportunity to address the important issue of reliability in dietary recall. Since the population is motivated, cooperative, and their addresses are known, we will be able to perform the proposed study economically. The findings of this study are potentially of major importance in the design and interpretation of results of case-control studies. This may ultimately have an important impact in clarification of the diet-cancer hypothesis.